There are many industrial uses of complex systems in which multiple and diverse electrical devices are electrically isolated, monitored and/or controlled by way of relay or relay-like circuits which may operate under the management control of a computer controller. By "controller" we refer to a management device such as a programmable digital processor which receives inputs in the form of electrical signals representing at least in part the conditions of a first class of real world electrical devices and which uses those inputs to create commands or outputs in the form of electrical signals which are applied directly or indirectly to a second class of real world electrical devices to determine the functional status thereof. The processor further relates or coordinates inputs to outputs according to a program defining the overall functions or function to be achieved by such devices in a complex system. By "real world" we refer to such devices as switches, solenoids and motors which are associated with work production and/or physical movement or other condition changes in an industrial system as opposed to mere calculations which might occur wholly within a data processor using only logic level signals. The controller may, as stated above, comprise at its heart a general purpose digital microprocessor chip capable of performing data processing and/or management tasks of many kinds. Alternatively, it may comprise a special purpose computer or even a hard wired circuit, the "program" portion of which is found in the form of hardware or firmware rather than the more traditional applications and operating system software. In general, however, complex systems in industrial applications of all kinds more and more typically include microprocessor chips which are not only flexible in operation and application, but are widely and inexpensively available from various sources and manufacturers such as Intel but are also widely and generally understood and used by engineers and technicians throughout the United States and the world.
An example of an industrial application comprising input type real world devices and output type real world devices operating in a complex system under the control of a data processor is a vehicle laundry wherein such operations as vehicle proximity detection, vehicle length and size assessment, soap spraying, water spraying, brushing, forced air drying, wheel washing and polishing are performed in spaced and overlapping sequences. In such a system, devices which provide condition or function-signaling inputs to a controller-programmer may include, by way of example and not by limitation, vehicle proximity detectors such as limit switches, wand switches and electric eyes, conveyor drive shaft angle encoders, emergency stop switches, keypads, coin boxes and a variety of other devices having contacts which create open and closed circuit conditions. Output or function-causing devices the excitation and operation of which are subject to a remote external control according to the management program found in a controller may include, by way of example and not by limitation, scrubbing brushes, air turbines, hydraulic and pneumatic cylinders, solenoids, pumps, lights, doors, wheel washers, motors and motor starting circuits.
In a more complex but nevertheless typical vehicle laundry it may be desirable to provide a variety of proffered service packages ranging from a simple wet wash to drying, waxing, the application of anti-corrosion agents and wheel washing. The customer may directly select such combinations by way of a credit card reader and keypad or may indirectly make such selections through an attendant who enters an appropriate code from a remote station and provides the customer with a coin or token or code input to simply initiate the operation of the system.
In addition various complex functions are or may be provided in a vehicle laundry such as vehicle proximity detection and vehicle size assessment thereby to schedule the energization and deenergization of various output devices in the system for the purpose of minimizing electrical energy consumption and cost.
In addition it is highly desirable to utilize a general purpose computer as part of the controller of a complex system in order that the general purpose digital computer be available for use in peripheral but related applications such as financial record keeping, maintenance record keeping and scheduling, payroll, employee attendance, machinery usage levels and other data collection and/or coordination functions which are typically associated with the conduct of a retail merchandizing operation. The general purpose computer may, however, be placed at the top of a hierarchy which includes lower order computers which are capable of independent action in the event the master computer experiences a failure or is temporarily unavailable.
Many other industrial applications of a complex nature involving input type electrical devices and output type electrical devices the energization and performance of which are to be coordinated by means of a controller will be apparent to those skilled in the art. Again by way of example and not by limitation, examples of such systems include baggage handling, conveyor systems, automated assembly systems, medical analysis and evaluation systems, access and security systems, construction machinery and other applications characterized by multiple operations on a common workpiece in sequential and coordinated fashion.
One of the problems associated with the construction and operation of complex systems operating under management of a computer-type controller is the typical need to customize electrical circuitry, particularly the interface circuitry which ties the real world electrical devices to the controller either as input devices or output devices. The devices themselves may vary as between simple input devices such as switches, and more complex and power-consuming output devices. In addition, the devices within a single class may vary widely as to excitation voltage and power consumption; e.g., a simple 100 watt filament type light bulb presents an entirely different electrical energization interfacing requirement than an induction motor that might be used to drive a high volume, high velocity air turbine.
Another problem confronting the control circuit designer is the desirability of providing not only for coordinated or integrated automatic control of the various controlled or output devices in a given system but also of providing for independent manual operation of selected devices and, moreover, of providing for overall operation in a coordinated fashion even though the master computer associated with the system may be down as a result of a malfunction or failure. It is doubtless a fact of life that many a complex and elegant computer controlled system has been rendered unproductive by reason of the failure of an inexpensive integrated circuit in a device upon which the overall system is dependent.